1. Field of the Invention
This invention relates generally to optical couplers and more particularly, to a new method of producing polished block type, single mode, evanescent wave directional couplers by means of mass production of the coupler halves.
2. Description of the Prior Art
Optical couplers are well known and various methods have been proposed to produce and assemble such couplers, especially single mode evanescent wave directional couplers.
In my prior U.S. patent application Ser. No. 700,281 filed on Feb. 11, 1985, the disclosure of which is incorporated herein by reference, there is disclosed an evanescent wave coupler having the important feature that in the coupler halves of which the assembled coupler is made, the fiber surface is positioned above or proud of the surface of the supporting substrate to enable fiber to fiber contact such that evanescent wave coupling occurs without the need for any interleaving material such as index matching oils and the assembly of the coupler is made simple as large surface areas are not required to be perfectly clean.
In the aforenoted patent application, there is disclosed a method of manufacture which illustrates the importance of the substrate hardness and the physical properties of the polishing lap which are the significant parameters in production of the coupler half having a proud fiber. However that method of manufacture was designed to produce coupler halves one at a time or as sets of coupler halves in a common substrate.
Another method has been proposed by Jaccard et al as reported in ECOC 83-9th European Conference on Optical Communications, Elsevier Science Publishers B.V. (North Holland), 1983, pp 409 to 412. The principle of the technique of Jaccard et al is based on the transfer of the in-plane submission accuracy provided by photolithography and anisotropic etching on silicon onto the mechanical etching of a collection of fibers via the preservation of the flatness of a polished side of a silicon wafer which is taken as a reference plane and used as a precise polishing stopper.
In the disclosed methods using a common substrate, there exists a need for great precision in the making of the grooves that support the fiber and also in the fixing of the fiber within the grooves in order that all of the coupler halves are identical. Further, it is necessary that the fiber core is well centered within the cladding and that there is no movement of the fiber with age within the groove for the above reason.